Revert "remove dead cmake code"

This reverts commit 14005fea48.

ortools/algorithms/python/CMakeLists.txt

@@ -30,3 +30,10 @@ endif()
 
 target_link_libraries(knapsack_solver_pybind11 PRIVATE ${PROJECT_NAMESPACE}::ortools)
 add_library(${PROJECT_NAMESPACE}::knapsack_solver_pybind11 ALIAS knapsack_solver_pybind11)
+
+if(BUILD_TESTING)
+  file(GLOB PYTHON_SRCS "*_test.py")
+  foreach(FILE_NAME IN LISTS PYTHON_SRCS)
+    add_python_test(FILE_NAME ${FILE_NAME})
+  endforeach()
+endif()